Eumetopias jubatus ssp. monteriensis

Eumetopias jubatus monteriensis has shown a steady increase in abundance (at an average growth rate of 4.3% (95% CL 1.9% – 7.3%) per year) for more than 30 years which is equivalent to three generations with new rookeries being established in southeast Alaska. The existing population is estimated to include about 65,000 animals. There are no threats currently limiting this population, and continued growth is anticipated until density dependent factors take effect. Therefore, E. j. monteriensis qualifies for listing by IUCN as Least Concern. The agency responsible for management of Steller Sea Lions in the United States, the National Marine Fisheries Service (NMFS), drafted a species status review which recommended that the eastern subspecies should be removed from the ESA threatened and endangered species list (NMFS 2012).

The Loughlin’s Northern Sea Lion population was estimated to number between 58,334 and 72,223 in 2009 (NMFS 2012). The most recent (2011) best estimate is 65,000 (NMFS unpublished data). Abundance declined in the 1950s and 1960s due to government sanctioned culling in British Columbia and Alaska. In the early 1970s laws were enacted to protect the species, and abundance has increased since then. Over the past three generations (30 years), abundance of E. j. monteriensis has increased by 170%, this increase is in marked contrast to the situation with western Steller Sea Lions that declined severely between1960 and 2000.

The majority of the breeding population is in the northern portion of the range with approximately 52% of the population in Southeast Alaska and 32% in British Columbia. Oregon (6%) and California (10%) contain the remainder of the population.

Eumetopias jubatus are the largest otariids and the fourth largest pinniped. Both sexes are robust and powerfully built. They are sexually dimorphic, with adult males weighing three times as much, and growing 20–25% longer than, adult females. Pups are born with a thick blackish-brown lanugo that is moulted by about six months of age. The maximum length of adult males is about 3.3 m and average weight is 1,000 kg. The maximum length for adult females is about 2.5 m and average weight is 273 kg. Pups are born at an average size of about 1 m and 18–22 kg (Loughlin 2009).

The age of sexual maturity is 3–6 years for females, and 3–7 years for males (Calkins and Pitcher 1982). Males are not able to defend territories before they are nine years old. The reproductive rate of Loughlin’s Northern Sea Lions is unknown, but the pregnancy rate of mature female western Steller Sea Lions was found to have declined during the 1970s and 1980s and was estimated to be 55% in the 1980s (Pitcher et al. 1998). Gestation lasts one year, including a delay of implantation of about three months. Females may live to be up to 30 years old and males to about 20 years (Loughlin 2009).

Loughlin’s Northern Sea Lions are highly polygynous and breed in the late spring and summer. Adult males arrive before females and those that are nine years or older establish themselves on territories, which they aggressively defend. Pups are born from May through July, and females stay continuously ashore with their newborns for the first 7–10 days after giving birth. Following this period of attendance, females make foraging excursions, primarily at night for periods of 18–25 hours, followed by time ashore to nurse their pup. Females come into oestrus and mate about two weeks after giving birth. Weaning can occur before the next breeding season, but it is not unusual to see females nursing yearlings or older juveniles (Loughlin 2009).

Loughlin’s Northern Sea Lions are primarily found from the coast to the outer continental shelf and slope. They sometimes leave haulouts in very large groups; however, sightings at sea are most often of groups of 1–12 animals. They aggregate in areas of prey abundance, including near fishing vessels, where they will feed on netted fish and discarded by-catch. Loughlin’s Northern Sea Lions have been known to move westward into the range if the western Steller Sea Lion, and some juvenile males have crossed the Gulf of Alaska to near Kodiak Island. They are not considered migratory; juveniles and subadults make the longest distance trips. Adults usually forage and live near their natal colonies and return to these sites to breed. The area used by adult females for foraging in winter increases dramatically over the area used in the summer and females tend to dive deeper in winter than summer. Diving is generally to depths of 200 m or less (Loughlin et al. 2003, Rehberg and Burns 2008). Dive duration is usually two minutes or less, with both parameters varying by season and age of the animal. Diving ability of pups and juveniles increases with age, and they routinely dive to depths of around 140 m for periods of two minutes as yearlings. The diving of adult males has not been studied.

Loughlin’s Northern Sea Lions feed on many varieties of fish and invertebrates. Much of the information on diet comes from animals living in southeast Alaska, where they feed on Walleye Pollock, Pacific Cod, flatfishes, rockfishes, herring, salmon, sand lance, skates, squid, and octopus (Trites et al. 2007). Adult females with young pups feed extensively at night, switching to foraging at any time after the breeding season. Sea Lions have been reported to kill and consume Harbor Seals in Glacier Bay National Park, Alaska.

The primary predators of sea lions are Killer Whales (Loughlin 2009). Sleeper Sharks in Alaska have been found with Sea Lion remains in their stomachs, but it is unknown whether the prey was killed or scavenged. Great White Sharks presumably take young animals in areas where their range overlaps.

The greatest threat to Loughlin’s Northern Sea Lions has been intentional culling in Southeast Alaska and Canada in the 1950s and 1960s. Those practices were discontinued in the early 1970s and the population has been increasing ever since. Some are killed in nets in fisheries off the west coast of North America. An unknown number may be shot during commercial fishing operations although it is generally believed that this source of mortality has been reduced dramatically since the establishment of federal laws prohibiting killing of sea lions in Canada and the United States (NMFS 2012). The 2008 Steller Sea Lion Recovery Plan found that there were no apparent threats limiting the recovery of this population, and the increasing population trend confirms that conclusion (NMFS 2008). 

Loughlin’s Northern Sea Lions are protected in the United States and Canada. In the U.S. they are listed as depleted under the Marine Mammal Protection Act. The entire species (E. jubatus) was listed as threatened under the ESA in 1990, and in 1997 the western population (corresponding to E. j. jubatus) was uplisted to endangered. A recovery plan for Steller Sea Lions was approved in 1992, and a revised recovery plan was published in 2008. Critical habitat was designated in 1993, including no entry zones near rookeries and management of fisheries activity in the vicinity of rookeries. Substantial funding has been made available for Steller Sea Lion research to develop information on ecology, behaviour, genetics, population dynamics, and movements. Results have been used to assist in the development of management activities, to attempt to understand the reasons for the decline of the western Steller Sea Lion, and to promote recovery of the species (NMFS 2008). In 2012, the agency responsible for management of sea lions in the U. S., the National Marine Fisheries Service, drafted a species status review which concluded that Loughlin’s Northern Sea Lions should be removed from the ESA threatened and endangered species list (NMFS 2012). 

Calkins, D. G. and Pitcher, K. W. 1982. Population assessment ecology and trophic relationships of Steller’s sea lions in the Gulf of Alaska. Environmental assessment of the Alaskan Continental shelf. U.S. Dept. of Commerce and U.S. Dept. of Interior, Final Reports of Principal Investigators, pp. 447-546.

Committee on Taxonomy. 2012. List of marine mammal species and subspecies. Available at: www.marinemammalscience.org. (Accessed: 7 May 2012.).

IUCN. 2012. IUCN Red List of Threatened Species (ver. 2012.2). Available at: http://www.iucnredlist.org. (Accessed: 17 October 2012).

Loughlin, T.R. 1997. Using the phylogeographic method to identify Steller sea lion stocks. In: A. Dizon, S.J. Chivers and W.F. Perrin (eds), Molecular Genetics of Marine Mammals, pp. 159–171. Society for Marine Mammalogy Special Publication 3, Lawrence, Kansas, USA.

Loughlin, T.R. 2009. Steller sea lion Eumetopias jubatus. In: W.F. Perrin, B. Wursig and J.G.M. Thewissen (eds), Encyclopedia of Marine Mammals, pp. 1107-1110. Academic Press.

Loughlin, T.R., Sterling, J.T., Merrick, R.L., Sease, J.L. and York, A.E. 2003. Immature Steller sea lion diving behavior. Fishery Bulletin 101: 566-582.

National Marine Fisheries Service. 2008. Recovery Plan for the Steller Sea Lion (Eumetopias jubatus). Revision. National Marine Fisheries Service, Silver Spring, Maryland, USA.

National Marine Fisheries Service. 2012. Draft Status Review of The Eastern Distinct Population Segment of Steller Sea Lion (Eumetopias jubatus). National Marine Fisheries Service, Juneau, Alaska, USA.

Phillips, C.D., Bickham, J.W., Patton, J.C. and Gelatt, T.S. 2009. Systematics of Steller sea lions (Eumetopias jubatus): subspecies recognition based on concordance of genetics and morphometrics. Occasional Papers, Museum of Texas Tech University 283: 1-15.

Pitcher, K.W., Calkins, D.G. and Pendleton, G.W. 1998. Reproductive performance of female Steller sea lions: an energetics-based reproductive strategy? Canadian Journal of Zoology 76: 2075-2083.

Rehberg, M.J. and Burns, J.M. 2008. Differences in diving and swimming behavior of pup and juvenile Steller sea lions (Eumetopias jubatus) in Alaska. Canadian Journal of Zoology 86: 539-553.

Trites, A. W., Calkins, D. G. and Winship, A. J. 2007. Diets of Steller sea lions (Eumetopias jubatus) in Southeast Alaska, 1993-1999. Fishery Bulletin 105: 234-248.